I ran them on my 80 years ago for wheeling here in the East, took them off when I started wheeling Moab etc. and never put them back on. I found they weren’t very effective in this area, seemed every limb was just long enough to catch the side of my truck and mirrors and too short for the limb riser to be effective, I think they would be more effective in a jungle and softer vegetation.
Being said, they were a simple black vinyl coated cable with one end wrapped around the front corner of the bull bar, the end ran through a loop, the other end a turnbuckle attached to a light bracket on a roof rack.
If I were to run them again, I would run a second cable a little farther outboard and to an antenna/light style mount in the tolerance between the hood and fender about 1/2 way or 2/3 of the way from the front to catch limbs that are just long enough to get under the first cable.
Good luck, good to hear you are wheeling the 21’, a better investment might be clear wrap on the sides!